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<p>Demonstration of <i>MDM2</i> amplification is currently recommended to confirm the diagnosis of well-differentiated adipocytic tumors arising in the retroperitoneum, abdomen, and pelvis; recurrent “lipomas”; those with equivocal cytologic atypia; deep extremity tumors &gt;10&#xa0;cm which lack cytologic atypia and occur in patients &gt;50&#xa0;years old, and in special clinical circumstances (Clay et al., 2015 [Clay criteria]). In our practice, fluorescence in situ hybridization studies (FISH) for <i>MDM2</i> were historically performed for all referred-in testing requests, for all well-differentiated fatty tumors &gt;10&#xa0;cm, and to confirm the diagnosis of atypical lipomatous tumor/well-differentiated liposarcoma (ALT/WDL) in cases with definite atypia. As part of a test utilization review, after exclusion of dedifferentiated liposarcoma, we reviewed 1151 ostensibly fatty tumors on which FISH was successfully performed. After exclusion of 203 cases for which testing was inappropriate or indicated for other reasons, 233/948 (24.6%) fatty tumors met at least one Clay criterion, and 222 (23.4%) had definite nuclear atypia. Among tumors with definite atypia, 152 (68.5%) were ALT/WDL, and 48 (21.6%) were spindle cell/pleomorphic lipoma arising in unusual locations or atypical spindle cell/pleomorphic lipomatous tumors. Thirty (12.9%) cases meeting any Clay criteria were ALT/WDL, and 4/453 (0.9%) tumors not meeting Clay criteria or having atypia were ALT/WDL. The sensitivity of Clay criteria plus nuclear atypia for ALT/WDL was 97.8%, while specificity was 62.7%. We conclude that it is safe to defer <i>MDM2</i> FISH in well-differentiated fatty tumors not meeting Clay criteria and lacking nuclear atypia.</p>

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Criteria for MDM2 fluorescence in situ hybridization testing in the diagnosis of well-differentiated adipocytic neoplasms: a retrospective utilization review of 1151 cases

  • 期刊论文

  • 发表日期：

    2025年11月21日

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  • Ashley N. Flaman,
  • Lingxin Zhang,
  • Brendan C. Dickson,
  • Elizabeth G. Demicco

摘要

Demonstration of MDM2 amplification is currently recommended to confirm the diagnosis of well-differentiated adipocytic tumors arising in the retroperitoneum, abdomen, and pelvis; recurrent “lipomas”; those with equivocal cytologic atypia; deep extremity tumors >10 cm which lack cytologic atypia and occur in patients >50 years old, and in special clinical circumstances (Clay et al., 2015 [Clay criteria]). In our practice, fluorescence in situ hybridization studies (FISH) for MDM2 were historically performed for all referred-in testing requests, for all well-differentiated fatty tumors >10 cm, and to confirm the diagnosis of atypical lipomatous tumor/well-differentiated liposarcoma (ALT/WDL) in cases with definite atypia. As part of a test utilization review, after exclusion of dedifferentiated liposarcoma, we reviewed 1151 ostensibly fatty tumors on which FISH was successfully performed. After exclusion of 203 cases for which testing was inappropriate or indicated for other reasons, 233/948 (24.6%) fatty tumors met at least one Clay criterion, and 222 (23.4%) had definite nuclear atypia. Among tumors with definite atypia, 152 (68.5%) were ALT/WDL, and 48 (21.6%) were spindle cell/pleomorphic lipoma arising in unusual locations or atypical spindle cell/pleomorphic lipomatous tumors. Thirty (12.9%) cases meeting any Clay criteria were ALT/WDL, and 4/453 (0.9%) tumors not meeting Clay criteria or having atypia were ALT/WDL. The sensitivity of Clay criteria plus nuclear atypia for ALT/WDL was 97.8%, while specificity was 62.7%. We conclude that it is safe to defer MDM2 FISH in well-differentiated fatty tumors not meeting Clay criteria and lacking nuclear atypia.